A flow battery that prevents discharge inhibition caused by lithium-containing deposits produced with chemical oxidation of mediator. Flow battery includes: anode including anode current collector having lithium element on a surface thereof; cathode including cathode current collector; separator disposed between anode and cathode; electrolyte including mediator having function as a redox couple; discharger including reductor and anode chamber, reductor being defined by separator, housing cathode and electrolyte and being configured to reduce the mediator, anode chamber housing the anode defined by separator; first flow channel and second flow channel, flow channels being connected to reductor; oxidizer connected to first and second flow channels; configured to chemically oxidize the mediator; circulator configured to circulate electrolyte to reductor, first flow channel, oxidizer and second flow channel in this order, wherein a trap configured to trap lithium-containing deposits produced with oxidation of mediator, disposed in part of the second flow channel or oxidizer.